package com.example.jdktest.test;

import java.util.HashMap;
import java.util.Hashtable;
import java.util.concurrent.ConcurrentHashMap;

/**
 * @author: dangwen
 * @createDate: 2021/2/25
 */
public class HashMapDemo {
    public static void main(String[] args) {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put("a", "b");
        System.out.println(hashMap.put("a", "c"));
        System.out.println(hashMap);
        Object o;
        Hashtable t;
        ConcurrentHashMap c;
    }
}
